This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

Locally rare species are expected to have a survival advantage because rarity reduces their risk of damage from pathogens. This "rare-species advantage" may help maintain plant diversity in natural systems and explain how introduced plant species become invasive weeds. Plant species are considered rare if few individuals are present; this assumes pathogens are specialized on individual species. In fact, most pathogens are able to infect a variety of different hosts and closely related species are more likely to share a pathogen. Thus rarity is not simply a function of species density (numerical rarity), but of the combined density of species with which it shares a pathogen. The PIs will evaluate the relative importance of phylogeny and abundance in the rare-species advantage in seven plant communities along the Central Coast of California. They will measure disease prevalence, host ranges of pathogens, and the ability of the pathogens to reproduce on different hosts. Results will be compared to local host abundance and relatedness between host species, in the first attempt to evaluate how the overall structure of a plant community affects the amount of disease suffered by each species in the community. The project will provide ecological training for a postdoctoral fellow with a background in molecular biology, as well as train graduate and undergraduate students in both molecular and ecological research. Continued support for the UCSC Forest Ecology Research Plot will help extend substantial educational and research synergies. This research will inform policies that regulate international trade of plants and plant products. Finally, the results will shed new light on whether introduced species systematically escape natural enemies, an idea that is highly influential in the biological control of weeds and other aspects of introduced species policy.